Ultra-heavy quasiparticles in metallic Nd2−yCeyCuO4

Abstract The specific heat C p ( T ) and the magnetic susceptibility χ ( T ) of compounds Nd 2− y Ce y CuO 4 , 0 ≤ y ≤ 0.2, were measured in the temperature range from 50 mK to 10 K. A Schottky anomaly in C p ( T ) for Nd 2 CuO 4 , resulting from the magnetic splitting of the Nd-4f ground state Kramers doublet due to exchange interactions with the ordered Cu moments, is broadened upon Ce doping, and the maximum is shifted to lower temperatures. In overdoped metallic compounds ( y = 0.2), the temperature dependence of C p ( T ) is linear below 300 mK with a large value of the coefficient γ ∼ 4 J/K 2 per mole Nd. A constant value of γ ( T ) in the same temperature range and the changes of C p ( T ) induced by an applied magnetic field corroborate the interpretation in terms of a heavy-fermion system due to the coupling between Nd moments and conduction electrons at the Cu sites.